PIM2 Kinase Regulates T-Cell Alloresponses and Graft-Versus-Host Disease in Mice

Allogeneic hematopoietic cell transplantation (HCT) can cure a variety of benign and malignant hematopoietic disorders, but graft-versus-host disease (GVHD) remains a significant source of transplant-related mortality and morbidity.  Mature T cells in donor stem cell graft are primarily responsible for the development of acute GVHD.  PIM kinases are a family of serine/threonine kinases, including PIM1, PIM2 and PIM3, which are expressed following T-cell activation. The PIM kinases have been shown to inhibit apoptosis as well as to stimulate the cell metabolism and protein synthesis.  In the current study, we investigated how PIM kinases regulate T-cell responses to alloantigens and GVHD development.  Using genetically modified mice on an FVB background that are deficient for either single, double, or triple kinases of the PIM family, we evaluated the role of PIM kinases on T-cell alloresponses. T cells deficient for PIM1/PIM3 kinases had reduced survival and proliferation upon stimulation with alloantigens in vitro, whereas T cells without the PIM2 kinase displayed increased survival and IFNγ production as compared to WT T cells.  After being transferred to lethally irradiated allogeneic mice in vivo, PIM1/PIM3 double knockout (KO) T cells had reduced expression of IFNγ in spleen, whereas PIM2 KO T cells showed decreased IL-4/5 expression, although similar IFNγ production when compared with WT T cells. These data suggest PIM2 kinase plays a distinct role by negatively regulating T-cell alloresponses. To test the role of PIM kinases on T-cell ability to induce GVHD, we transferred WT, PIM2 single KO, PIM1/PIM2 double KO, PIM1/PIM3 double KO, PIM2/PIM3 double KO, or PIM1/PIM2/PIM3 triple KO T cells together with WT bone marrow cells into lethally irradiated B6 mice.  While PIM1/PIM3 double KO T cells induced milder GVHD, PIM2 KO T cells induced much more severe GVHD when compared to WT T cells.  In addition, any types of T cells deficient for PIM2 caused significantly more severe GVHD than their PIM2-replete counterparts.  Furthermore, restoration of PIM2 expression by gene transfection reduced the ability of PIM2-deficient T cells in the induction of GVHD.  Enhanced pathogenicity of PIM2-deficient T cells was also confirmed in another murine model of allogeneic HCT.  These results indicate that PIM2 plays a dominant role among PIM kinases in negatively regulating T-cell alloresponses and GVHD induction.  To validate the data obtained from KO mice, we silenced the PIM2 kinase in PIM1/PIM3 KO T cells by administration of a PIM kinase pan-inhibitor (AZD, AstraZeneca R&D, Waltham, MA), and we observed exacerbated GVHD induced by PIM1/PIM3 KO T cells after PIM2 kinase silencing. Our study demonstrates the important result that PIM2 negatively regulates T-cell mediated alloresponse and GVHD development.  The finding uncovers a novel biological function of PIM kinases as well as urges caution in inhibiting PIM kinases for the treatment of hematologic malignances in patients after allogeneic HCT.

YW and AD contributed equally to this work.